Microscale Flow Patterning

The ability to manipulate fluids at the microscale is a key element of
any lab-on-a-chip platform, enabling core functionalities such as liquid
mixing, splitting and transport of molecules and particles.
Lab-on-a-chip devices are commonly divided in two main families:
continuous phase devices, and discrete phase (droplets) devices. While a
large number of mechanisms are available for precise control of
droplets on a large scale, microscale control of continuous phases
remains a substantial challenge. In a traditional continuous-flow
microfluidic device, fluids are pumped actively (e.g. by pressure
gradients, electro-osmotic flow) or passively (e.g. capillary driven)
through a fixed microfluidic network, making the device geometry and
functionality intimately dependent on one another (e.g. DLD, inertial
mixer, H-separator, etc.). The advent of on-chip microfluidic valves
brought more flexibility in routing fluids through microfluidic
networks, adding a dynamic dimension to the static geometrical network.
However, the number of degrees of freedom of valve-based systems is
restricted by their dependence on bulky pneumatic lines (regulators,
pressure systems, controllers), which are difficult to scale down in
size and cost. In this talk I will present our ongoing work leveraging
non-uniform EOF and thermocapillary flows to control flow patterns in
microfluidic chambers. By setting the spatial distribution of surface
potential or a spatial temperature distribution, we demonstrate the
ability to dictate desired flow patterns without the use of physical
walls. We believe that such flow control concepts will help break the
existing link between geometry and functionality, bringing new
capabilities to on-chip analytical methods.